System and method for intracoding video data

ABSTRACT

A video system for coding a stream of video data that includes a stream of video frames divides each video frame into a matrix of a plurality of subblocks, wherein each subblock includes a plurality of pixels. The video system operates in accordance with nine prediction modes. Each prediction mode determines a prediction mode according to which a present subblock is to be coded. One of the nine prediction modes is selected to encode the present subblock, wherein the selected prediction mode provides for a minimum error value in the present subblock.

CLAIM OF PRIORITY

This is a continuation of U.S. patent application Ser. No. 15/245,975,filed on Aug. 24, 2016, now patented as U.S. Pat. No. 9,930,343, issuedon Mar. 27, 2018, which is a continuation of U.S. patent applicationSer. No. 14/140,349, filed on Dec. 24, 2013, now patented as U.S. Pat.No. 9,432,682, issued on Aug. 30, 2016, which is a divisional of U.S.patent application Ser. No. 13/679,957, filed on Nov. 16, 2012, nowpatented as U.S. Pat. No. 8,908,764, issued on Dec. 9, 2014, which iscontinuation of U.S. patent application Ser. No. 12/767,744, filed onApr. 26, 2010, now patented as U.S. Pat. No. 8,385,415, issued on Feb.26, 2013, which is continuation of U.S. patent application Ser. No.10/848,992, filed on May 18, 2004, now patented as U.S. Pat. No.7,706,444, issued on Apr. 27, 2010, which is a continuation of U.S.patent application Ser. No. 09/732,522, filed on Dec. 6, 2000, nowpatented as U.S. Pat. No. 6,765,964, issued on Jul. 20, 2004, which arehereby incorporated by reference in their entireties for all purposes.

BACKGROUND OF THE INVENTION Field of the Invention

The invention pertains to a video system that compresses video data fortransmission or storage and decompresses the video data for display.More particularly, the invention pertains to a video system and a methodfor intracoding video data.

Description of the Related Art

Video systems transmit, process and store large quantities of videodata. To create a video presentation, such as a video movie, a renderingvideo system displays the video data as a plurality of digital images,also referred to as “frames,” thereby simulating movement. In order toachieve a video presentation with an acceptable video quality, or toenable transmission and storage at all, a conventional video systemmodifies the video data prior to transmission or storage. For instance,the video system compresses and encodes the video data to reduce the bitrate for storage and transmission.

In a conventional video system a video encoder is used to compress andencode the video data and a video decoder is used to decompress and todecode the video data. The video encoder outputs video data that has areduced bit rate and a reduced redundancy. That is, the technique ofvideo compression removes spatial redundancy within a video frame ortemporal redundancy between consecutive video frames.

The video encoder and video decoder may be configured to apply one oftwo types of coding to compress the video stream, namely intracoding andintercoding. These two types of coding are based on the statisticalproperties of the video frames. When the video frames are coded usingintracoding, the compression is based on information contained in asingle frame (the frame that is compressed) by using the spatialredundancy within the frame. Intracoding, thus, does not depend on anyother frames. In contrast, intercoding uses at least one other frame asa reference and codes a difference between the frame to be compressedand the reference frame. Intercoding is thus based on a temporalredundancy between consecutive frames in the video data.

The field of video compression is subject to international standards,e.g., International Telecommunications Union (ITU) standard H.263 thatdefines uniform requirements for video coding and decoding. In addition,manufacturers of video coders and decoders modify or build upon theinternational standards and implement proprietary techniques for videocompression.

Despite the existence of the international standards and the proprietarytechniques, there is still a need for improved techniques for videocompression. For example, as the quality of a displayed video moviedepends directly from the technique used for video compression, anyimprovement of the video compression technique makes the video moviemore pleasing for the viewer.

SUMMARY OF THE INVENTION

An aspect of the invention involves a method of coding a stream of videodata including a stream of video frames. The method divides each videoframe into a matrix of a plurality of subblocks, wherein each subblockincludes a plurality of pixels. The method further defines nineprediction modes, wherein each prediction mode determines a modeaccording to which a present subblock is to be coded. The method furtherselects one of the nine prediction modes to encode the present subblock.The selected prediction mode provides for a minimum error value in thepresent subblock.

Another aspect of the invention involves a video system for coding anddecoding a stream of video data that includes a stream of video frames.The video system includes a video encoder and a mode selector. The videoencoder is configured to receive a stream of video data including astream of video frames and to divide each video frame into a matrix of aplurality of subblocks, wherein each subblock includes a plurality ofpixels. The mode selector is in communication with the video encoder andis configured to define nine prediction modes. Each prediction modedetermines a mode according to which a present subblock is to be coded.The mode selector is further configured to select one of the nineprediction modes to encode the present subblock, wherein the selectedprediction mode provides for a minimum error value in the presentsubblock.

Once the video system has selected the best prediction mode to encodethe pixels of the present subblock, the video system encodes the minimumerror value and transmits the encoded minimum error value within acompressed bitstream to the decoder. The minimum error value representsa difference between predicted pixels of the present subblock and theoriginal pixels of the subblock. The decoder uses the predicted pixelsand the difference to the original pixels to accurately reconstruct thevideo frame.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, advantages, and novel features of the inventionwill become apparent upon reading the following detailed description andupon reference to the accompanying drawings.

FIG. 1 is a high-level block diagram of a system for video applicationshaving an encoding side and a decoding side.

FIG. 2 is a high-level illustration of a frame and its division inmacroblocks and subblocks.

FIG. 3 is a subblock illustrating the directions according to which thesubblock can be encoded, wherein each direction represents one of eightprediction modes in accordance with the present invention.

FIG. 4 is a flow chart in accordance with an embodiment of the presentinvention that selects a prediction mode.

FIG. 5 is an illustration of three neighboring subblocks, wherein twosubblocks are used to encode the third subblock.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description, reference is made to the accompanyingdrawings, which form a part hereof, and which show, by way ofillustration, specific embodiments in which the invention may bepracticed. It is to be understood that other embodiments may be utilizedand structural changes may be made without departing from the scope ofthe present invention. Where possible, the same reference numbers willbe used throughout the drawings to refer to the same or like components.Numerous specific details are set forth in order to provide a thoroughunderstanding of the present invention. However, it will be obvious toone skilled in the art that the present invention may be practicedwithout the specific details or with certain alternative equivalentdevices and methods to those described herein. In other instances,well-known methods, procedures, components, and devices have not beendescribed in detail so as not to unnecessarily obscure aspects of thepresent invention.

FIG. 1 is a high-level block diagram of a video compression anddecompression system 1 (hereinafter “video system 1”) having an encoderapparatus 3 and a decoder apparatus 5 that is coupled to the encoderapparatus 3 through a medium 9. The encoder apparatus 3 includes a videoencoder 2, a mode selector 14 and a buffer 8. The decoder apparatus 5includes a buffer 10, a video decoder 12 and a mode selector 16. Theencoder apparatus 3 receives a video sequence 20 (VIDEO IN) and encodesthe video sequence 20 to generate an encoded and thus compressedrepresentation in one of a number of possible formats. The format may bein an interleaved format tailored for “live” streaming of the encodedrepresentation. The format may also be in a single file format in whicheach of the encoded representation is stored in a contiguous blockwithin one file.

The video sequence 20 input to the encoder apparatus 3 may be either alive signal, e.g., provided by a video camera, or a prerecorded sequencein a predetermined format. The video sequence 20 includes frames of adigital video, an audio segment consisting of digital audio,combinations of video, graphics, text, and/or audio (multimediaapplications), or analog forms of the aforementioned. If necessary,conversions can be applied to various types of input signals such asanalog video, or previously compressed and encoded video to produce anappropriate input to the encoder apparatus 3. In one embodiment, theencoder apparatus 3 may accept video in RGB or YUV formats. The encoderapparatus 3, however, may be adapted to accept any format of input aslong as an appropriate conversion mechanism is supplied. Conversionmechanisms for converting a signal in one format to a signal in anotherformat are well known in the art.

The medium 9 may be a storage device or a transmission medium. In oneembodiment, the video system 1 may be implemented on a computer. Theencoder apparatus 3 sends an encoded video stream (representation) tothe medium 9 that is implemented as a storage device. The storage devicemay be a video server, a hard disk drive, a CD rewriteable drive, aread/write DVD drive, or any other device capable of storing andallowing the retrieval of encoded video data. The storage device isconnected to the decoder apparatus 5, which can selectively read fromthe storage device and decode the encoded video sequence. As the decoderapparatus 5 decodes a selected one of the encoded video sequence, itgenerates a reproduction of the video sequence 20, for example, fordisplay on a computer monitor or screen.

In another embodiment, the medium 9 provides a connection to anothercomputer, which may be a remote computer, that receives the encodedvideo sequence. The medium 9 may be a network connection such as a LAN,a WAN, the Internet, or the like. The decoder apparatus 5 within theremote computer decodes the encoded representations contained thereinand may generate a reproduction of the video sequence 20 on a screen ora monitor of the remote computer.

Aspects of the video system 1 illustrated in FIG. 1 and described abovecan be combined and supplemented to achieve other embodiments. Numerousother implementations are consistent with the scope of this invention.Such other implementations need not be restricted to video, but mayinclude audio or other forms of media as well.

Pre-existing video encoding techniques typically break up a frame(picture) into smaller blocks of pixels called macroblocks. Eachmacroblock can consist of a matrix of pixels, typically a 16×16 matrix,defining the unit of information at which encoding is performed. Thematrix of pixels is therefore referred to as a 16×16 macroblock. Thesevideo encoding techniques usually break each 16×16 macroblock further upinto smaller matrices of pixels. For example, into 8×8 matrices ofpixels or 4×4 matrices of pixels. Such matrices are hereinafter referredto as subblocks. In one embodiment of the present invention, a 16×16macroblock is divided into 16 4×4 subblocks. Those skilled in the artwill appreciate that the present invention is equally applicable tosystems that use 8×8 subblocks, 4×4 subblocks or only 16×16 macroblockswithout breaking it up into subblocks.

Further, the pre-existing encoding techniques provide for motioncompensation and motion estimation using motion vectors. The motionvectors describe the direction, expressed through an x-component and ay-component, and the amount of motion of the 16×16 macroblocks, or theirrespective subblocks, and are transmitted to the decoder as part of thebit stream. Motion vectors are used for bidirectionally encoded pictures(B-pictures) and predicted pictures (P pictures) as known in the art.

The video encoder 2 performs a discrete cosine transform (DCT) to encodeand compress the video sequence 20. Briefly, the video encoder 2converts the video sequence 20 from the spatial, temporal domain intothe frequency domain. The output of the video encoder 2 is a set ofsignal amplitudes, called “DCT coefficients.” A quantizer receives theDCT coefficients and assigns each of a range (or step size) of DCTcoefficient values a single value, such as a small integer, duringencoding. Quantization allows data to be represented more compactly, butresults in the loss of some data. Quantization on a finer scale resultsin a less compact representation (higher bit-rate), but also involvesthe loss of less data. Quantization on a more coarse scale results in amore compact representation (lower bit-rate), but also involves moreloss of data. The mode selector 14 communicates with the video encoder 2and monitors and controls encoding of the video sequence 20. The modeselector 14 determines in accordance with the present inventionprediction modes according to which the video encoder 2 encodes thevideo sequence 20. The mode selector 14 may be a processor or a softwaremodule that are configured to operates in accordance with a method ofthe present invention. FIG. 1 shows the mode selector 14 forillustrative purposes as an element separate from the video encoder 2.Those skilled in the art will appreciate that the functionality of themode selector 14 may be combined with the functionality of the videoencoder 2.

The buffer 8 of the encoder apparatus 3 receives the encoded andcompressed video sequence (hereinafter “encoded video sequence”) fromthe video encoder 2 and adjusts the bit rate of the encoded videosequence before it is sent to the medium 9. Buffering may be requiredbecause individual video images may contain varying amounts ofinformation, resulting in varying coding efficiencies from image toimage. As the buffer 8 has a limited size, a feedback loop to thequantizer may be used to avoid overflow or underflow of the buffer 8.The bit-rate of the representation is the rate at which therepresentation data must be processed in order to present therepresentation in real time.

The decoder apparatus 5 performs the inverse function of the encoderapparatus 3. The buffer 10 serves also to adjust the bit rate of theincoming encoded video sequence. The video decoder 12 decodes anddecompresses in combination with the mode selector 16 the incoming videosequence reconstructing the video sequence. The mode selector 16determines the prediction modes according to which the video encoder 2encoded the incoming video sequence. The decoder apparatus 5 outputs adecoded and decompressed video sequence 24 illustrated as “VIDEO OUT”(hereinafter “decoded video sequence 24”).

The video decoder 12 receives a bit stream that represents the encodedvideo sequence from the buffer 10 (FIG. 1). In one embodiment, the videodecoder is a conventional video decoder, e.g., a MPEG-2 decoder, thatincludes a decoder controller, a VLC decoder (Variable Length Coding,VLC) and a reconstruction module. The operation and function of thesecomponents are known to those skilled in the art. These components areknown to those skilled in the art and described in generally availableMPEG documents and publications.

FIG. 2 is a diagram illustrating a video frame 30 that is part of thevideo sequence 20. As described above, known video encoding techniquestypically break up a video frame 30 into macroblocks 36, 36 a, 36 b, 36c, 36 d. For example, the video frame 30 is divided into a matrix of16×16 macroblocks 36, 36 a, 36 b, 36 c, 36 d. The video system 1 encodesthe macroblocks 36, 36 a, 36 b, 36 c, 36 d line by line, from top tobottom and from left to right, as indicated through a dashed line 34that illustrates the sequence of, e.g., intra encoding. In theillustrated embodiment, the dashed line 34 ends at the macroblock 36 a,which is the next macroblock to be encoded. All prior macroblocks 36, 36b, 36 c, 36 d have already been encoded.

The macroblock 36 a, as a representative for all macroblocks 36, 36 a,36 b, 36 c, 36 d, is shown in greater detail below the video frame 30.The video encoding technique of the video system 1 breaks eachmacroblock 36, 36 a, 36 b, 36 c, 36 d further up into a matrix of pixels38, hereinafter referred to as a subblock 38. In one embodiment, thesubblock 38 is a 4×4 matrix of pixels, wherein the 16 pixels are labeledas a, b, c, p. Bordering pixels of an adjacent subblock of a neighboringmacroblock 36 b, which is located above the macroblock 36 a, are labeledas A, B, C, D. Further, bordering pixels of a subblock located above andto the right of the macroblock 36 a are labeled as E, F, G, H. Likewise,bordering pixels of an adjacent subblock of a neighboring macroblock 36c, which is located to the left of the macroblock 36 a, are labeled asI, J, K, L. Bordering pixels of a subblock located below and to the leftof the macroblock 36 a are labeled as M, N, O, P. A bordering pixel of asubblock of a macroblock 36 d, which is located above and to the left ofthe macroblock 36 a, is labeled as Q.

The video system 1 of the present invention codes each macroblock 36 asan intra macroblock. Intra macroblocks are transform encoded withoutmotion compensated prediction. Thus, intra macroblocks do not referencedecoded data from either previous or subsequent frames. An I-frame is aframe consisting completely of intra macroblocks. Thus, I-frames areencoded with no reference to previous or subsequent frames. I-frames arealso known as “Intra-frames.”

FIG. 3 is a subblock 38 illustrating possible directions according towhich the subblock 38 may be encoded. In accordance with the presentinvention, the subblocks of a macroblock 36, 36 a, 36 b, 36 c, 36 d canbe intra coded in one of nine modes (Modes 0, Mode 1, . . . , Mode 9) aslisted hereinafter. That is, a particular subblock 38 may be predictedfrom a subblock above the current subblock that is currently decoded(“vertical prediction”), from the subblock to the left of the currentsubblock (“horizontal prediction”), or from both the left and the abovesubblocks (“diagonal prediction”). The Modes 1-8 predict the subblock ina predetermined direction and the Mode 0 uses a uniform average withoutprediction in a predetermined direction. In FIG. 3, each directionrepresents one of the eight prediction modes in accordance with thepresent invention.

Mode 0:

In this mode, each pixel a-p is predicted by the following equation:

$a,b,c,d,\ldots\mspace{14mu},{p = {\frac{A + B + C + D + I + J + K + L + 4}{8}.}}$

It is contemplated that in this mode as well as in the following modes,a “division” means to round the result down toward “minus infinity”(−∞). For instance, in mode 0, the term “+4” ensures that the divisionresults in a rounding to the nearest integer. This applies also theother modes.

If four of the pixels A-P are outside the current picture (frame) thatis currently encoded, the average of the remaining four pixels is usedfor prediction. If all eight pixels are outside the picture, theprediction for all pixels in this subblock is 128. A subblock maytherefore always be predicted in mode 0.

Mode 1:

If the pixels A, B, C, D are inside the current picture, the pixels a-pare predicted in vertical direction as shown in FIG. 3. That is, thepixels a-p are predicted as follows:

a, e, i, m = A b, f, j, n = B c, g, k, o = C d, h, l, p = DMode 2:

If the pixels I, J, K, L are inside the current picture, the pixels a-pare predicted in horizontal direction. That is, the pixels a-p arepredicted as follows:

a, b, c, d = I e, f, g, h = J i, j, k, l = K m, n, o, p = LMode 3:

This mode is used if all pixels A-P are inside the current picture. Thiscorresponds to a prediction in a diagonal direction as shown in FIG. 3.The pixels a-p are predicted as follows:

m = (J + 2K + L + 2)/4 i, n = (I + 2J + K + 2)/4 e, j, o = (Q + 2I + J +2)/4 a, f, k, p = (I + 2Q + A + 2)/4 b, g, l = (Q + 2A + B + 2)/4 c, h =(A + 2B + C + 2)/4 d = (B + 2C + D + 2)/4Mode 4:

This mode is used if all pixels A-P are inside the current picture. Thisis also a diagonal prediction.

a = (A + 2B + C + I + 2J + K + 4)/8 b, e = (B + 2C + D + J + 2K + L +4)/8 c, f, i = (C + 2D + E + K + 2L + M + 4)/8 d, g, j, m = (D + 2E +F + L + 2M + N + 4)/8 h, k, n = (E + 2F + G + M + 2N + O + 4)/8 l, o =(F + 2G + H + N + 2O + P + 4)/8 p = (G + H + O + P + 2)/4Mode 5:

This mode is used if all pixels A-P are inside the current picture. Thisis also a diagonal prediction.

a, j = (Q + A + 1)/2 b, k = (A + B + 1)/2 c, l = (B + C + 1)/2 d = (C +D + 1)/2 e, n = (I + 2Q + A + 2)/4 f, o = (Q + 2A + B + 2)/4 g, p = (A +2B + C + 2)/4 h = (B + 2C + D + 2)/4 i = (Q + 2I + J + 2)/4 m = (I +2J + K + 2)/4Mode 6:

This mode is used if all pixels A-P are inside the current picture. Thisis a diagonal prediction.

a = (2A + 2B + J + 2K + L + 4)/8 b, i = (B + C + 1)/2 c, j = (C + D +1)/2 d, k = (D + E + 1)/2 l = (E + F + 1)/2 e = (A + 2B + C + K + 2L +M + 4)/8 f, m = (B + 2C + D + 2)/4 g, n = (C + 2D + E + 2)/4 h, o = (D +2E + F + 2)/4 p = (E + 2F + G + 2)/4Mode 7:

This mode is used if all pixels A-P are inside the current picture. Thisis a diagonal prediction.

a = (B + 2C + D + 2I + 2J + 4)/8 b = (C + 2D + E + I + 2J + K + 4)/8 c,e = (D + 2E + F + 2J + 2K + 4)/8 d, f = (E + 2F + G + J + 2K + L + 4)/8g, i = (F + 2G + H + 2K + 2L + 4)/8 h, j = (G + 3H + K + 2L + M + 4)/8k, m = (G + H + L + M + 2)/4 l, n = (L + 2M + N + 2)/4 o = (M + N + 1)/2p = (M + 2N + O + 2)/2Mode 8:

This mode is used if all pixels A-P are inside the current picture. Thisis a diagonal prediction.

a, g = (Q + I + 1)/2 b, h = (I + 2Q + A + 2)/4 c = (Q + 2A + B + 2)/4 d= (A + 2B + C + 2)/4 e, k = (I + J + 1)/2 f, l = (Q + 2I + J + 2)/4 i, o= (J + K + 1)/2 j, p = (I + 2J + K + 2)/4 m = (K + L + 1)/2 n = (J +2K + L + 2)/2

In one embodiment of the present invention, a mode selection algorithmdetermines a criteria to select one of the nine modes. The subblock 38is then encoded in accordance with the selected mode. The mode selectionalgorithm is described in detail below.

FIG. 4 is a flow chart of a procedure illustrating the method inaccordance with the present invention that codes video data including astream of video frames and that selects one of the prediction modesModes 0-8. In one embodiment, the method codes a luminance portion (Y)of a video frame.

In a step 28, e.g., when a user activates the video system 1, theprocedure initializes the video system 1. The initialization procedureincludes, for example, determining whether the encoder apparatus 3 isoperating and properly connected to receive the stream of video frames.

In a step 30, the procedure receives the stream of video frames anddivides each video frame into a matrix of a plurality of subblocks,wherein each subblock includes a plurality of pixels. The matrix of aplurality of subblocks may include 4×4 subblocks 38 that are part of amacroblock as described above.

In a step 32, the procedure defines the nine prediction modes Mode 0-8,wherein each prediction mode determines a mode according to which apresent subblock is to be coded. For example, the procedure may executea subroutine to calculate and define the modes Mode 0-8.

In a step 34, the procedure selects one of the nine prediction modesMode 0-8 to encode the present subblock 38. In one embodiment, theprocedure calculates for each mode an error value, determines which modeprovides a minimum error value and selects that mode for encoding thepresent subblock 38.

Once the procedure has selected the “best” prediction mode to encode thepixels of the present subblock 38, the procedure encodes the minimumerror value and transmits the encoded minimum error value within acompressed bitstream to the decoder. The minimum error value representsa difference between the predicted pixels of the present subblock andthe original pixels of the subblock. The difference may be encoded usinga DCT, coefficient quantization and variable length coding as known inthe art. The decoder uses the predicted pixels and the difference to theoriginal pixels to accurately reconstruct the video frame. The procedureends at a step 36.

The procedure provides that each of the 4×4 subblocks 38 is coded inaccordance with one of the nine prediction modes Mode 0-8. As this mayrequire a considerable number of bits if coded directly, the videosystem 1 in accordance with the present invention may apply a moreefficient way of coding the mode information. A prediction mode of asubblock is correlated with the prediction modes of adjacent subblocks.

FIG. 5 illustrates this through three exemplary subblocks A, B, C. Thesubblock C is the subblock that is to be encoded (predicted) with thehelp of the subblocks A, B whose prediction modes are known. Thesubblock A is located above the subblock C and the subblock B is locatedleft of the subblock C. In this case, an ordering of the most probable,next most probable etc. prediction mode for the subblock C is given. Anexample of such an ordering table is listed hereinafter. The table isdivided into ten groups (Group 1-Group 10). In each group, therespective prediction mode for the subblock A is constant (e.g., Mode 0of the subblock A is constant in Group 2), and the prediction mode forthe subblock B varies. That is, the (constant) prediction mode for thesubblock A within a group may be combined with one of the nineprediction modes for the subblock B within that group.

For each combination of the prediction modes of the subblocks A and B, asequence of nine numbers is given, one number for each of the nine Modes0-9. For example in Group 3, if the prediction modes for the subblock Aand the subblock B are both Mode 1, a string “1 6 2 5 3 0 4 8 7”indicates that the Mode 1, i.e., the first number in the string, is themost probable mode for the subblock C. The Mode 6, i.e., the secondnumber in the string, is the next most probable mode. In the exemplarystring, the Mode 7 is the least probable since the number 7 is the lastnumber in the string. The string will be part of the stream of bits thatrepresents the encoded video sequence.

The stream of bits therefore includes information (Prob0=1 (see Table1)) indicating the mode used for the subblock C. For example, theinformation may indicate that the next most probable intra predictionmode is Mode 6. Note that a “-” in the table indicates that thisinstance cannot occur. The term “outside” used in the Table 1 indicates“outside the frame.” If the subblock A or B is within the frame, but isnot INTRA coded (e.g., in a P frame, the subblock C could be INTRA codedbut either the subblock A or the subblock B may not be INTRA coded),there is no prediction mode. The procedure of the present inventionassumes the Mode 0 for such subblocks.

TABLE 1 B A = outside outside 0 - - - - - - - - mode 0 0 2 - - - - - - -mode 1 - - - - - - - - - mode 2 2 0 - - - - - - - mode3 - - - - - - - - - GROUP 1 mode 4 - - - - - - - - - mode5 - - - - - - - - - mode 6 - - - - - - - - - mode 7 - - - - - - - - -mode 8 - - - - - - - - - B A = mode 0 outside 0 1 - - - - - - - mode 0 02 1 6 4 8 5 7 3 mode 1 1 0 2 6 5 4 3 8 7 mode 2 2 8 0 1 7 4 3 6 5 mode 32 0 1 3 8 5 4 7 6 GROUP 2 mode 4 2 0 1 4 6 7 8 3 5 mode 5 0 1 5 2 6 3 84 7 mode 6 0 1 6 2 4 7 5 8 3 mode 7 2 7 0 1 4 8 6 3 5 mode 8 2 8 0 1 7 34 5 6 B A = mode 1 outside 1 0 - - - - - - - mode 0 1 2 5 6 3 0 4 8 7mode 1 1 6 2 5 3 0 4 8 7 mode 2 2 1 7 6 8 3 5 0 4 mode 3 1 2 5 3 6 8 4 70 GROUP 3 mode 4 1 6 2 0 4 5 8 7 3 mode 5 1 5 2 6 3 8 4 0 7 mode 6 1 6 02 4 5 7 3 8 mode 7 2 1 7 6 0 8 5 4 3 mode 8 1 2 7 8 3 4 5 6 0 B A = mode2 outside - - - - - - - - - mode 0 0 2 1 8 7 6 5 4 3 mode 1 1 2 0 6 5 74 8 3 mode 2 2 8 7 1 0 6 4 3 5 mode 3 2 0 8 1 3 7 5 4 6 GROUP 4 mode 4 20 4 1 7 8 6 3 5 mode 5 2 0 1 5 8 4 6 7 3 mode 6 2 0 6 1 4 7 8 5 3 mode 72 7 8 1 0 5 4 6 3 mode 8 2 8 7 1 0 4 3 6 5 B A = mode 3outside - - - - - - - - - mode 0 0 2 1 3 5 8 6 4 7 mode 1 1 0 2 5 3 6 48 7 mode 2 2 8 1 0 3 5 7 6 4 mode 3 3 2 5 8 1 4 6 7 0 GROUP 5 mode 4 4 20 6 1 5 8 3 7 mode 5 5 3 1 2 8 6 4 0 7 mode 6 1 6 0 2 4 5 8 3 7 mode 7 27 0 1 5 4 8 6 3 mode 8 2 8 3 5 1 0 7 6 4 B A = mode 4outside - - - - - - - - - mode 0 2 0 6 1 4 7 5 8 3 mode 1 1 6 2 0 4 5 37 8 mode 2 2 8 7 6 4 0 1 5 3 mode 3 4 2 1 0 6 8 3 5 7 GROUP 6 mode 4 4 26 0 1 5 7 8 3 mode 5 1 2 5 0 6 3 4 7 8 mode 6 6 4 0 1 2 7 5 3 8 mode 7 27 4 6 0 1 8 5 3 mode 8 2 8 7 4 6 1 3 5 0 B A = mode 5outside - - - - - - - - - mode 0 5 1 2 3 6 8 0 4 7 mode 1 1 5 6 3 2 0 48 7 mode 2 2 1 5 3 6 8 7 4 0 mode 3 5 3 1 2 6 8 4 7 0 GROUP 7 mode 4 1 62 4 5 8 0 3 7 mode 5 5 1 3 6 2 0 8 4 7 mode 6 1 6 5 2 0 4 3 7 8 mode 7 27 1 6 5 0 8 3 4 mode 8 2 5 1 3 6 8 4 0 7 B A = mode 6outside - - - - - - - - - mode 0 1 6 2 0 5 4 3 7 8 mode 1 1 6 5 4 2 3 07 8 mode 2 2 1 6 7 4 8 5 3 0 mode 3 2 1 6 5 8 4 3 0 7 GROUP 8 mode 4 6 41 2 0 5 7 8 3 mode 5 1 6 5 2 3 0 4 8 7 mode 6 6 1 4 0 2 7 5 3 8 mode 7 27 4 6 1 5 0 8 3 mode 8 2 1 6 8 4 7 3 5 0 B A = mode 7outside - - - - - - - - - mode 0 2 0 4 7 6 1 8 5 3 mode 1 6 1 2 0 4 7 58 3 mode 2 2 7 8 0 1 6 4 3 5 mode 3 2 4 0 8 3 1 7 6 5 GROUP 9 mode 4 4 27 0 6 1 8 5 3 mode 5 2 1 0 8 5 6 7 4 3 mode 6 2 6 4 1 7 0 5 8 3 mode 7 27 4 0 8 6 1 5 3 mode 8 2 8 7 4 1 0 3 6 5 B A = mode 8outside - - - - - - - - - mode 0 2 0 8 1 3 4 6 5 7 mode 1 1 2 0 6 8 5 73 4 mode 2 2 8 7 1 0 3 6 5 4 mode 3 8 3 2 5 1 0 4 7 6 GROUP 10 mode 4 20 4 8 5 1 7 6 3 mode 5 2 1 0 8 5 3 6 4 7 mode 6 2 1 6 0 8 4 5 7 3 mode 72 7 8 4 0 6 1 5 3 mode 8 2 8 3 0 7 4 1 6 5

The information about the prediction modes may be efficiently coded bycombining prediction mode information of two subblocks 38 in onecodeword. The stream of bits includes then the resulting codewords,wherein each codeword represents the prediction modes of the twosubblocks. Table 2 lists exemplary binary codewords for code numbers(Code No.) between 0 and 80. The probability of a mode of the firstsubblock is indicated as Prob0 and the probability of a mode of thesecond subblock is indicated as Prob1.

TABLE 2 Code No. Prob0 Prob1 Codeword 0 0 0 1 1 0 1 001 2 1 0 011 3 1 100001 4 0 2 00011 5 2 0 01001 6 0 3 01011 7 3 0 0000001 8 1 2 0000011 92 1 0001001 10 0 4 0001011 11 4 0 0100001 12 3 1 0100011 13 1 3 010100114 0 5 0101011 15 5 0 000000001 16 2 2 000000011 17 1 4 000001001 18 4 1000001011 19 0 6 000100001 20 3 2 000100011 21 1 5 000101001 22 2 3000101011 23 5 1 010000001 24 6 0 010000011 25 0 7 010001001 26 4 2010001011 27 2 4 010100001 28 3 3 010100011 29 6 1 010101001 30 1 6010101011 31 7 0 00000000001 32 0 8 00000000011 33 5 2 00000001001 34 43 00000001011 35 2 5 00000100001 36 3 4 00000100011 37 1 7 0000010100138 4 4 00000101011 39 7 1 00010000001 40 8 0 00010000011 41 6 200010001001 42 3 5 00010001011 43 5 3 00010100001 44 2 6 00010100011 451 8 00010101001 46 2 7 00010101011 47 7 2 01000000001 48 8 1 0100000001149 5 4 01000001001 50 4 5 01000001011 51 3 6 01000100001 52 6 301000100011 53 8 2 01000101001 54 4 6 01000101011 55 5 5 01010000001 566 4 01010000011 57 2 8 01010001001 58 7 3 01010001011 59 3 7 0101010000160 6 5 01010100011 61 5 6 01010101001 62 7 4 01010101011 63 4 70000000000001 64 8 3 0000000000011 65 3 8 0000000001001 66 7 50000000001011 67 8 4 0000000100001 68 5 7 0000000100011 69 4 80000000101001 70 6 6 0000000101011 71 7 6 0000010000001 72 5 80000010000011 73 8 5 0000010001001 74 6 7 0000010001011 75 8 60000010100001 76 7 7 0000010100011 77 6 8 0000010101001 78 8 70000010101011 79 7 8 0001000000001 80 8 8 0001000000011

With the nine prediction modes (Table 1) and the probabilities of themodes (Table 1, Table 2), a mode selection algorithm determines the modeaccording to which a particular subblock is predicted. In one embodimentof the present invention, the algorithm selects the mode using a sum ofabsolute differences (SAD) between the pixels a-p and the correspondingpixels in the original frame, and the above probabilities of the modes.The SAD and the probability table are used to select the mode for aparticular subblock 38. The algorithm calculates a parameter uError foreach of the nine possible modes Mode 0-8. The mode that provides thesmallest uError is the mode selected for the subblock 38.

The uError is calculated as follows:uError=SAD({a, . . . ,p},{original frame})+rd_quant[uMBQP]*uProb,

where SAD({a, . . . , p},{original frame} is the sum of absolutedifference between the pixels a-p and the corresponding pixels in theoriginal frame,

where rd_quant[uMBQP] is a table of constant values indexed by aquantization parameter uMBQP. uMBQP is given byconst U8rd_quant[32]=(1,1,1,1,1,1,2,2,2,2,3,3,3,4,4,5,5,6,7,7,8,9,11,12,13,15,17,19,21,24,27,30);and

where uProb is the probability of the mode occurring, provided by theposition in the mode probability table (Table 1).

For example, the prediction mode for the subblocks A is the Mode 1 andthe prediction mode for the subblock B is the Mode 1. The string “1 6 25 3 0 4 8 7” indicates that the Mode 1 is also the most probable modefor the subblock C. The Mode 6 is the second most probable mode, etc.Thus, when the algorithm calculates uError for the Mode 0, theprobability uProb is 5. Further, for the Mode 1 the probability uProb is0, for the Mode 2 the probability uProb is 2, for the Mode 3 theprobability uProb is 4, and so forth.

In addition to coding the luminance portion (Y) of the video frame, thevideo system 1 of the present invention may also predict the chrominanceportions (U, V) of the video frame. The chrominance portions may beconsidered as chrominance planes (U and V-planes). Typically, thechrominance planes (U and V-planes) are a quarter of the size of aluminance plane. Thus, in a 16×16 macroblock a corresponding 8×8 blockof pixels exists in both the U and V-planes. These 8×8 blocks aredivided into 4×4 blocks. In general, separate prediction modes are nottransmitted for chrominace blocks. Instead, the modes transmitted forthe Y-plane blocks are used as prediction modes for the U and V-planeblocks.

While the above detailed description has shown, described and identifiedseveral novel features of the invention as applied to a preferredembodiment, it will be understood that various omissions, substitutionsand changes in the form and details of the described embodiments may bemade by those skilled in the art without departing from the spirit ofthe invention. Accordingly, the scope of the invention should not belimited to the foregoing discussion, but should be defined by theappended claims.

The invention claimed is:
 1. A method of decoding video data in acomputing system, the method comprising: decoding a present subblock ofa video frame according to an intra prediction mode that specifies apredicted value of an upper right-hand corner pixel of the presentsubblock based at least in part on a weighted average of a plurality ofpixel values comprising a value of a lower right-hand corner pixel of avertically adjacent subblock, a value of a lower left-hand corner pixelof an upper-right diagonally adjacent subblock, a value of a pixelimmediately horizontally-right adjacent to the lower left-hand cornerpixel of the upper-right diagonally adjacent subblock, a value of alower right-hand corner pixel of a horizontally adjacent subblock, avalue of an upper right-hand corner pixel of a lower-left diagonallyadjacent subblock, and a value of a pixel immediately vertically-downadjacent to the upper right-hand corner pixel of the lower-leftdiagonally adjacent subblock.
 2. The method of claim 1, wherein theintra prediction mode specifies the predicted value, P(d), of the upperright-hand corner pixel of the present subblock according to:P(d)=(D+2E+F+L+2M+N+4)/8 wherein D comprises the value of the lowerright-hand corner pixel of the vertically adjacent subblock, E comprisesthe value of the lower left-hand corner pixel of the upper-rightdiagonally adjacent subblock, F comprises the value of the pixelimmediately horizontally-right adjacent to the lower left-hand cornerpixel of the upper-right diagonally adjacent subblock, L comprises thevalue of the lower right-hand corner pixel of the horizontally adjacentsubblock, M comprises the value of the upper right-hand corner pixel ofthe lower-left diagonally adjacent subblock, and N comprises the valueof the pixel immediately vertically-down adjacent to the upperright-hand corner pixel of the lower-left diagonally adjacent subblock.3. The method of claim 1, wherein each of the present subblock, thevertically adjacent subblock, the upper-right diagonally adjacentsubblock, the horizontally adjacent subblock, and the lower-leftdiagonally adjacent subblock comprises a rectangular array of pixellocations.
 4. The method of claim 1, wherein the intra prediction modefurther specifies a predicted value of a pixel down-left diagonally fromthe upper right-hand corner pixel of the present subblock equal to thepredicted value of the upper right-hand corner pixel of the presentsubblock.
 5. The method of claim 1, wherein the intra prediction modecomprises a first diagonal prediction mode of a plurality of availableintra prediction modes, wherein the plurality of available intraprediction modes further comprises a horizontal prediction mode and avertical prediction mode.
 6. The method of claim 5, wherein theplurality of available intra prediction modes further comprises fiveother diagonal prediction modes.
 7. The method of claim 1, furthercomprising: receiving a compressed bitstream comprising compressed videoframes defined by subblocks comprising the present subblock, thevertically adjacent subblock, the upper-right diagonally adjacentsubblock, the horizontally adjacent subblock, and the lower-leftdiagonally adjacent subblock.
 8. A non-transitory computer-readablemedium including one or more instructions that, when executed by amachine, cause the machine to: decode a present subblock of a videoframe according to an intra prediction mode that specifies a predictedvalue of an upper right-hand corner pixel of the present subblock basedat least in part on a weighted average of a plurality of pixel valuescomprising a value of a lower right-hand corner pixel of a verticallyadjacent subblock, a value of a lower left-hand corner pixel of anupper-right diagonally adjacent subblock, a value of a pixel immediatelyhorizontally-right adjacent to the lower left-hand corner pixel of theupper-right diagonally adjacent subblock, a value of a lower right-handcorner pixel of a horizontally adjacent subblock, a value of an upperright-hand corner pixel of a lower-left diagonally adjacent subblock,and a value of a pixel immediately vertically-down adjacent to the upperright-hand corner pixel of the lower-left diagonally adjacent subblock.9. The non-transitory computer-readable medium of claim 8, wherein theintra prediction mode specifies the predicted value, P(d), of the upperright-hand corner pixel of the present subblock according to:P(d)=(D+2E+F+L+2M+N+4)/8 wherein D comprises the value of the lowerright-hand corner pixel of the vertically adjacent subblock, E comprisesthe value of the lower left-hand corner pixel of the upper-rightdiagonally adjacent subblock, F comprises the value of the pixelimmediately horizontally-right adjacent to the lower left-hand cornerpixel of the upper-right diagonally adjacent subblock, L comprises thevalue of the lower right-hand corner pixel of the horizontally adjacentsubblock, M comprises the value of the upper right-hand corner pixel ofthe lower-left diagonally adjacent subblock, and N comprises the valueof the pixel immediately vertically-down adjacent to the upperright-hand corner pixel of the lower-left diagonally adjacent subblock.10. The non-transitory computer-readable medium of claim 8, wherein eachof the present subblock, the vertically adjacent subblock, theupper-right diagonally adjacent subblock, the horizontally adjacentsubblock, and the lower-left diagonally adjacent subblock comprises arectangular array of pixel locations.
 11. The non-transitorycomputer-readable medium of claim 8, wherein the intra prediction modefurther specifies a predicted value of a pixel down-left diagonally fromthe upper right-hand corner pixel of the present subblock equal to thepredicted value of the upper right-hand corner pixel of the presentsubblock.
 12. The non-transitory computer-readable medium of claim 8,wherein the intra prediction mode comprises a first diagonal predictionmode of a plurality of available intra prediction modes, wherein theplurality of available intra prediction modes further comprises ahorizontal prediction mode and a vertical prediction mode.
 13. Thenon-transitory computer-readable medium of claim 8, further comprisingone or more instructions that, when executed by the machine, cause themachine to: receive a compressed bitstream comprising compressed videoframes defined by subblocks comprising the present subblock, thevertically adjacent subblock, the upper-right diagonally adjacentsubblock, the horizontally adjacent subblock, and the lower-leftdiagonally adjacent subblock.
 14. An apparatus, comprising: circuitry toreceive at least a portion of a bitstream of video data; and circuitryto decode a present subblock of a video frame according to an intraprediction mode that specifies a predicted value of an upper right-handcorner pixel of the present subblock based at least in part on aweighted average of a plurality of pixel values comprising a value of alower right-hand corner pixel of a vertically adjacent subblock, a valueof a lower left-hand corner pixel of an upper-right diagonally adjacentsubblock, a value of a pixel immediately horizontally-right adjacent tothe lower left-hand corner pixel of the upper-right diagonally adjacentsubblock, a value of a lower right-hand corner pixel of a horizontallyadjacent subblock, a value of an upper right-hand corner pixel of alower-left diagonally adjacent subblock, and a value of a pixelimmediately vertically-down adjacent to the upper right-hand cornerpixel of the lower-left diagonally adjacent subblock.
 15. The apparatusof claim 14, wherein the intra prediction mode specifies the predictedvalue, P(d), of the upper right-hand corner pixel of the presentsubblock according to:P(d)=(D+2E+F+L+2M+N+4)/8 wherein D comprises the value of the lowerright-hand corner pixel of the vertically adjacent subblock, E comprisesthe value of the lower left-hand corner pixel of the upper-rightdiagonally adjacent subblock, F comprises the value of the pixelimmediately horizontally-right adjacent to the lower left-hand cornerpixel of the upper-right diagonally adjacent subblock, L comprises thevalue of the lower right-hand corner pixel of the horizontally adjacentsubblock, M comprises the value of the upper right-hand corner pixel ofthe lower-left diagonally adjacent subblock, and N comprises the valueof the pixel immediately vertically-down adjacent to the upperright-hand corner pixel of the lower-left diagonally adjacent subblock.16. The apparatus of claim 14, wherein each of the present subblock, thevertically adjacent subblock, the upper-right diagonally adjacentsubblock, the horizontally adjacent subblock, and the lower-leftdiagonally adjacent subblock comprises a rectangular array of pixellocations.
 17. The apparatus of claim 14, wherein the intra predictionmode further specifies a predicted value of a pixel down-left diagonallyfrom the upper right-hand corner pixel of the present subblock equal tothe predicted value of the upper right-hand corner pixel of the presentsubblock.
 18. The apparatus of claim 14, wherein the intra predictionmode comprises a first diagonal prediction mode of a plurality ofavailable intra prediction modes, wherein the plurality of availableintra prediction modes further comprises a horizontal prediction modeand a vertical prediction mode.
 19. The apparatus of claim 18, whereinthe plurality of available intra prediction modes further comprises fiveother diagonal prediction modes.
 20. The apparatus of claim 14, furthercomprising a buffer to store the portion of the bitstream.